<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
</head>
<body ng-app="myApp">
	<div  ng-controller="OuterCtrl">
		<span ng-bind="a"></span>
		<div ng-controller="InnerCtrl">
			<span ng-bind="a"></span>
			<span ng-bind="b"></span>
			<button ng-click="increase()">increase a</button>
		</div>
	</div>
	<script src="http://cdn.bootcss.com/angular.js/1.6.6/angular.js"></script>
	<script>
		var app = angular.module("myApp", [])
		app.controller("OuterCtrl", function($scope){
			$scope.a = 1;
		})
		app.controller("InnerCtrl", function($scope){
			$scope.b = 100;

			$scope.increase = function(){
				$scope.a++;
			}
		})
	</script>
</body>
</html>